Culinary ware produced from thermally-tempered glasses having compositions within the general soda-lime-silica field is well-known to the art. Because the coefficient of thermal expansion of soda lime glasses is relatively high, their use in cooking ware requires such articles to be thermally tempered to substantially enhance their mechanical strength and, in so doing, improve the thermal shock resistance thereof.
The incorporation of inorganic colorants into glass batches to impart an integral coloration therein has been long practiced in the glass art. A history of the use of colorants in glass plus an explanation of various reaction mechanisms involved in the development of colors therein can be found in Coloured Glasses, Woldemar A. Weyl, Dawson's of Pall Mall, London, 1959.
Consumer purchasing of culinary and dinnerware is frequently greatly influenced by the aesthetic appearance of the ware, with color being one of the most potent factors affecting such purchasing. The consumer market for plants and plant growing supplies and accessories is a large and presently rapidly expanding business. Studies have indicated that glass containers perform as well as, and in some instances better than, ceramic or plastic containers for growing plants. In like manner to food service ware, the purchase of flowerpots can be strongly influenced by the appearance thereof.
Extensive opinion testing of consumers, utilizing target samples prepared by applying clear tinted lacquers of various colors and shades on transparent glass bodies, resulted in a particular brownish tint being deemed the most attractive by a significant majority of the persons interviewed. Coincidentally, this color is quite similar to a commercially-marketed line of culinary ware prepared from borosilicate glass compositions. This circumstance presented the economically advantageous challenge to duplicate the color of the borosilicate glasses in a soda-lime composition, generally a very difficult objective to accomplish, in order to provide complementary product lines.
Research was then undertaken to devise glass compositions in the soda-lime-silica system which, when thermally tempered for improved mechanical strength and thermal shock resistance, would visually match the color and transmittance of the target samples. Such glasses could be useful in numerous applications, particularly in food service ware and containers for growing plants. Transmittance measurements of the desired product yielded a curve having a configuration such as that appearing in the appended drawing. Visually, the color of the glass can be described as an amber-with-rose-highlights hue.